Effects of tDCS on motor learning and memory formation: a consensus and critical position paper

Abstract

Motor skills are required for activities of daily living. Transcranial direct current stimulation (tDCS) applied in association with motor skill learning has been investigated as a tool for enhancing training effects in health and disease. Here, we review the published literature investigating whether tDCS can facilitate the acquisition and retention of motor skills and adaptation. A majority of reports focused on the application of tDCS with the anode placed over the primary motor cortex (M1) during motor skill acquisition, while some evaluated tDCS applied over the cerebellum during adaptation of existing motor skills. Work in multiple laboratories is under way to develop a mechanistic understanding of tDCS effects on different forms of learning and to optimize stimulation protocols. Efforts are required to improve reproducibility and standardization. Overall, reproducibility remains to be fully tested, effect sizes with present techniques are moderate (up to d= 0.5) (Hashemirad, Zoghi, Fitzgerald, & Jaberzadeh, 2016) and the basis of inter-individual variability in tDCS effects is incompletely understood. It is recommended that future studies explicitly state in the Methods the exploratory (hypothesis-generating) or hypothesis-driven (confirmatory) nature of the experimental designs. General research practices could be improved with prospective pre-registration of hypothesisbased investigations, more emphasis on the detailed description of methods (including all pertinent details to enable future modeling of induced current and experimental replication) and use of post-publication open data repositories. A checklist is proposed for reporting tDCS investigations in a way that can improve efforts to assess reproducibility.

Gender differences in cognitive Theory of Mind revealed by transcranial direct current stimulation on medial prefrontal cortex

“…The relative small number of subjects and the lack of a control task condition represent further potential limitations. Furthermore, an important discussion surrounding tDCS research is related to how reproducibility of reported effects should be evaluated49. A recent review50 on the effects of tDCS on social cognition pointed out that some studies produced results inconsistent to each other, likely due to methodological differences (e.g., intensity and duration of the stimulation, online vs. offline stimulation, electrode size, scalp placement, study design, experimental task).…”

Remotely Supervised Transcranial Direct Current Stimulation Increases the Benefit of At-Home Cognitive Training in Multiple Sclerosis

“…It is theorized that pairing tDCS with rehabilitation strategies may lead to more meaningful and lasting benefit (10)(11)(12)(13)(14). A particularly promising application of tDCS is to improve the rate of learning (15)(16)(17) and magnitude of benefit from cognitive training (CT) (14,(18)(19)(20)(21)(22)(23)(24)(25)(26). While many questions remain, pairing tDCS with CT has been shown to increase learning and cognitive performance, particularly in tasks of information processing and working memory (14,18,22,(26)(27)(28)(29).…”

Methodology for tDCS integration with fMRI

“…However, despite encouraging results in human neurophysiological experiments (Nitsche & Paulus, 2000;Stagg & Nitsche, 2011), clinical trials Bikson et al, 2016;Boggio et al, 2008;Brunoni et al, 2013;Fregni et al, 2006;Lefaucheur et al, 2017;Valle et al, 2009) and detailed characterization of its physiological mechanisms of action in animal models (Bikson et al, 2004;Ironside et al, 2018;Jackson et al, 2016;O'Shea & Revol, 2017), questions remain about protocol optimization, especially as relating to inter-and intra-individual variability (Chew, Ho, & Loo, 2015;Dyke, Kim, Jackson, & Jackson, 2016;Horvath, Vogrin, Carter, Cook, & Forte, 2016;Lopez-Alonso, Fernandez-Del-Olmo, Costantini, Gonzalez-Henriquez, & Cheeran, 2015;Worsching et al, 2017). The integration of tDCS with modern neuroimaging techniques (Saiote, Turi, Paulus, & Antal, 2013;Turi, Paulus, & Antal, 2012) is likely to represent a key methodological approach for advancing our understanding of the functional correlates of tDCS mechanisms in terms of changes in patterns of brain activation and for understanding individual differences in response to stimulation (Buch et al, 2017;Esmaeilpour et al, 2018;Giordano et al, 2017).…”